The present invention relates to a vertical magnetic head with integrated coil and its manufacturing process.
It finds privileged application in video recording by the general public. But it may also be used in other areas, such as data backup or computer memories.
A magnetic recording medium for video recording, data backup or computer memory comprises numerous tracks on which information is written in the form of magnetic fields.
To increase information density, not only can the amount of information per unit length be increased, but also the number of tracks. To achieve this purpose, track width is reduced and, simultaneously, the distance between them is reduced until the tracks abut one another.
To avoid any crosstalk problems on reading, the information on two adjacent tracks is written at opposite angles. The head angle must be most precise (for example 20xc2x10.15xc2x0 in the new so-called DVC standard or  less than  less than Digital rodeo Cassette  greater than  greater than .
To meet these requirements, so-called  less than  less than sandwich  greater than  greater than  heads can be currently found on the market of which an example of embodiment is illustrated in FIG. 1 appended hereto. The head shown comprises a substrate 2 carrying a magnetic circuit 4 made up of a magnetic layer placed on the top surface of the substrate, this circuit having two polar parts 5 and 7 at the front separated by an air gap 6 which is formed by a nonmagnetic spacer. This head also comprises, above the magnetic circuit, a nonmagnetic substrate 2xe2x80x2. An opening 8 is pierced through the whole unit to allow the passage of a conductor coil 9 surrounding the magnetic circuit.
The head shown in FIG. 1 is intended to co-operate with a recording medium S oriented perpendicular to the substrate (in other words parallel to the latter""s edge)
Such heads may be described as  less than  less than vertical  greater than  greater than  in the sense that the active surface is perpendicular to the general surface of the substrate.
The width of the air gap, called 1, is calculated perpendicular to the substrate (parallel to the recording medium). This Width 1 substantially corresponds to the respective width of the tracks in the medium. The length of the air gap, called L, is calculated in the direction of the relative movement of the head and recording medium. The height of the air gap, called h, is calculated parallel to the surface of the substrate carrying the magnetic circuit.
As soon as track width becomes narrow (less than approximately 10 micrometers), these heads become very difficult to fabricate (problems relating to precision alignment of the two polar parts during glass welding, low efficiency due to magnetic circuit length, difficult coil production, which is an added part and cannot be adapted easily to a package production process etc.)
The abstract of Japanese patent, vol. 13, No. 98 (P-840) (3446) of Mar. 8, 1989, describes a different magnetic head with planar coiling. This head is shown in FIG. 2 appended hereto. It comprises two polar parts 12a, 12b separated by an air gap 13, a twin spiral coil 14a, 14b placed over the two limbs of the magnetic circuit, two connection pads 15a, 15b and a magnetic bridge 15 closing the magnetic circuit.
This head still has disadvantages connected firstly with its coil structure which is long and therefore resistant producing thermal noise and, secondly with its magnetic circuit which is relatively long and therefore has reduced efficiency.
EP-A-0,467,263 discloses a head which partly avoids these drawbacks. This type of head can be seen in appended FIGS. 3 and 4. They show a nonmagnetic substrate 21, a first insulating layer 22, a second insulating layer 29, a magnetic circuit 30, a conductor coil 38 of solenoid type wound Ground the magnetic circuit; electric connection strips 33 and connection pads 34.
FIG. 4 also shows the two front polar parts 25 and 27 separated by an air gap g. Also, an insulating layer 35 covering the entire unit and a protective layer 36 or superstrate complete the unit and make the contact surface symmetrical with the recording medium.
Although satisfactory from certain viewpoints, it this structure has the disadvantage of giving rise to a very large head thickness in the zone lying between substrate 21 and superstrate 36. Such thickness corresponds to the lower part of coil 33, polar parts 25, 27 and insulating layers 22, 29, 32, 35. This thickness may give rise to friction problems with the recording medium leading to problems of differential wear of the various materials. Moreover, this large thickness gives rise to a considerable risk of delamination or bulging owing to intrinsic constraints in the layers, constraints of thermal origin etc.
Also, the process for manufacturing a head in accordance with FIGS. 3 and 4 is hardly compatible with package processes, in particular for the production of the azimuth for the air gap using a diamond instrument, or for certain planarization stages of the insulators deposited on large thicknesses of metallic patterns, which leads to problems of step overlay with breaks on the edge of the patterns.
The purpose of the present invention is precisely to remedy such drawbacks.
For this purpose, the invention suggests integrating part of the coil winding into she substrate, namely the lower sheet of conductors. In practice, the lower sheet is placed in a chamber made in the substrate. In this way, the head thickness can be reduced and, correlatively, the problems described above come to be solved.
In precise manner, the purpose of the invention is a vertical magnetic head comprising a solid substrate, a magnetic circuit with at east one first and one second polar part placed side by side and separated by a nonmagnetic air gap, this magnetic circuit comprising at least one non-embedded part in the substrate, a conductor coil surrounding that part of the magnetic circuit which is not embedded in the substrate, this head being characterized in that the conductor coil is formed by a lower sheet of conductors placed in at least one chamber made in the substrate and by an upper sheet of conductors astride the non-embedded part.
According to a first embodiment, the magnetic circuit comprises a rear magnetic closing part and a first and second side magnetic part magnetically connected to the rear magnetic closing part and to the first and second polar parts respectively, the first and second side magnetic parts each forming a non-embedded part of the magnetic circuit, and characterized in that the conductor coil comprises at least one winding coiled around at least the first and/or second side magnetic parts, this winding comprising a lower sheet of conductors passing under the first and/or second side magnetic parts, this lower sheet being integrated into the substrate, and an upper sheet astride the first and/or second side polar parts.
The side magnetic parts are directly connected to the other components of the magnetic circuit (rear closing part and polar parts) or via an insulating layer of controlled thickness (for example SiO2 or alumina 0.1 to 0.2 xcexcm thick). The use of an insulating layer is preferable for high frequency operation.
Advantageously, the polar parts are also integrated into the substrate.
Still preferably, the rear magnetic closing part is also integrated into the substrate.
If the substrate is not in insulating material, either because it is conductive or semi-conductive, the integration of the lower sheet of conductors can be achieved by etching said chambers in the substrate, said chambers being filled with insulating material in which the conductors are subsequently fabricated. This is the case in particular for a silicone substrate.
In another embodiment, the magnetic circuit comprises a rear closing part forming the non-embedded part of the circuit, and the conductor coil comprises a winding coiled around this rear closing part, with a lower sheet of conductors passing under the rear closing part, this lower sheet being embedded in the substrate, and an upper sheet passing over the rear closing part.
Advantageously, the rear closing part is magnetically connected to the first and second polar parts, there being no side magnetic parts.
In this alternative, the first and second polar parts may be embedded in the substrate.
According to a further embodiment, the first and second polar parts form the part of the magnetic circuit that is not embedded in the substrate, and the conductor coil surrounds at least one of the said first and second polar parts, this conductor coil comprising a lower sheet of conductors passing under at least one of the polar parts and being embedded in the substrate, and an upper sheet of conductors astride at least one of the polar parts.
A further object of the present invention is a process for manufacturing a vertical magnetic head such as just described. This process consists of, on a solid substrate, forming a magnetic circuit with a first and second polar part placed side by side and separated by a nonmagnetic air gap, this magnetic circuit comprising at least one part non-embedded in the substrate, and of forming a conductor winding around the non-embedded part of the circuit, this process being characterized in that said conductor winding is formed by making a lower sheet of conductors in at least one chamber made in the substrate and passing under the non-embedded part, and by embedding this lower sheet in the substrate, and by forming an upper sheet of conductors astride the non-embedded part of the magnetic circuit.
The process of the invention comprises the methods of use corresponding to the modes of embodiment of the head (forming a magnetic circuit with only one rear closing part, or with no rear part).